The present invention relates generally to operations performed and equipment utilized in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a slickline signal filtering apparatus and associated methods.
A slickline rig is commonly used to perform operations in a subterranean well. One advantage of using slickline rigs is that they are relatively inexpensive to maintain and operate. Another advantage is that, due to the relatively small size of a slickline rig, it may be readily and conveniently transported and installed at a wellsite.
One function typically performed by a slickline rig is that of depth correlation. A tool known as a casing collar locator is conveyed through a casing string in a well suspended from a metal line (the slickline) spooled on the slickline rig. The casing collar locator generates a magnetic field and, as the collar locator passes through a casing collar, the increased metal mass causes a corresponding increase in a magnetic force (due to the magnetic field) biasing the collar locator into contact with the casing string.
This increased magnetic force in turn causes an increase in tension in the slickline attached to the collar locator. The increased tension is sensed at the surface by a load cell or other force sensor on the slickline rig. In this manner, an operator at the surface can detect when the collar locator passes through a casing collar and, since the depth of each casing collar is known, the depth of the collar locator (and any other tools conveyed on the slickline) may be determined.
Unfortunately, the signal obtained from the force sensor on the slickline rig is typically contaminated with noise, which sometimes makes it difficult to accurately discern the increased tension due to the collar locator passing through a casing collar. The noise may be a result of any number of contributing factors, for example, due to the environment about the slickline rig, due to characteristics of the rig itself, etc. This makes it very difficult to isolate the slickline from vibrations, etc. which alter the tension measured in the slickline by the force sensor.
It will, thus, be readily appreciated that it would be highly desirable to reduce or eliminate the noise present in the contaminated signal output by the force sensor. This would permit more accurate casing collar detection in the signal, which would enable more accurate depth correlation. Furthermore, the reduction or elimination of noise in the force sensor signal would permit the signal to be used for data transmission, for example, to transmit pressure and temperature measurements via slickline tension modulation.